<style>
  * {
    padding: 0;
    margin: 0;
  }

  body {
    background: #34495e;
  }

  main {
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
  }

  ul {
    list-style: none;
    display: flex;
    justify-content: space-evenly;
    width: 200px;
  }

  ul li {
    position: relative;
  }

  ul li strong {
    background: #e67e22;
    color: #2c3e50;
    padding: 2px 20px;
    cursor: pointer;
    text-transform: uppercase;
  }

  ul li strong+div {
    border: solid 2px #e67e22;
    display: flex;
    flex-direction: column;
    padding: 10px 20px;
    position: absolute;
    transform-origin: left top;
    /* transform: scale(1); */
    transform: scale(0);

    z-index: -1;
    transition: .6s;
    background: #e67e22;
  }

  ul li strong+div a {
    display: inline-block;
    padding: 5px;
    font-size: 1em;
    color: #2c3e50;
    text-decoration: none;
    text-transform: uppercase;
  }

  ul li:hover strong+div {
    transform: scale(1);
  }
</style>

<main>
  <ul>
    <li>
      <strong>backend</strong>
      <div>
        <a href="">PHP</a>
        <a href="">golang</a>
        <a href="">python</a>
      </div>
    </li>
    <li>
      <strong>frontend</strong>
      <div>
        <a href="">javascript</a>
        <a href="">css</a>
        <a href="">html</a>
      </div>
    </li>
  </ul>
</main>